Humidity responsive device



T. K. KJELLMAN ETAL 3,123,687

HUMIDITY RESPONSIVE DEVICE March 3, 1964 3 Sheets-Sheet 1 Filed April 13, 1962 THOMAS K. KJELLMAN FRANK O WATSON INVENTORS ATTORNEYS March 3, 1964 "r. K. KJELLMAN ETAL 3,123,637

HUMIDITY RESPONSIVE DEVICE Filed April 15, 1962 s Sheets-Sheet 2 THOMAS K.KJELLMAN FRANK O. WATSON I N VE NTORS A TTOR/VE Y5 T. K. KJELLMAN ETAL 3,123,687

HUMIDITY RESPONSIVE DEVICE 5 Sheets-Sheet 3 March 3, 1964 Filed April 13, 1962 THOMAS K.KJELLMAN.

FRANK o. WATSON.

INVENTORS (Kim; ATTORNEYS.

United States Patent 3,123,687 HUMIDITY RESPONSIVE DEVICE Thomas K. Kjellman, Timonium, and Frank 0. Watson, Baltimore, Md., assignors to The Bendix Corporation, Baltimore, Md., a corporation of Delaware Filed Apr. 13, 1962, Ser. No. 187,273 2 Claims. (Ci. 200--61.06)

This invention relates to humidity responsive devices, and more particularly to a humidity responsive device including means for providing a strain release for the humidity responsive element.

Moisture responsive elements typically consist of a small cable of human hair which is kept under tension. It is possible for the calibrating mechanism to impose so much force on these hair elements that a destructive limit is exceeded. To avoid this, a strain release spring may be at one end of the element but the introduction of such a spring creates its own problems. The coil springs often used have considerable thickness and may take up more room that is available. They also have the characteristic of imposing a force on the hair element which varies with the setting of the calibrating mechanism, thus introducing an error into the response of the humidity element. It is, therefore, an object of the present invention to provide an improved humidity responsive device having a strain release spring etfectively connected to the humidity element which spring has a substantially constant spring force and therefore does not interpose a significant error in the calibration.

It is another object of the present invention to provide a humidity responsive device having a strain release spring which meets the above objective while requiring minimum volume within the device.

It is a further object of the present invention to provide a humidity responsive device which meets the above objectives and is so arranged that it may be mounted on a standard electrical wall junction box with a minimum of thickness of depth extending outside of said junction box.

Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings in which:

FIG. 1 is a plan view of our humidity control device as seen from the front with the control knob and decorative cover plate removed;

FIG. 1A is a View of the device of FIG. 1 taken from the front with part of the mounting plate broken away and the protective cover for the humidity element removed to show more detail of the internal mechanism;

FIG. 2 is a sectional view of the device of FIG. 1 taken on line 2-2 of FIG. 1; and

FIG. 3 is a sectional view of the device of FIG. 2, taken on line 33 of FIG. 2.

Referring now to FIG. 1, our humidity responsive device includes a mounting plate having attached at its back a resilient mounting member 12 (shown in dotted outline) which includes holes 14, 14' for receiving screws to be attached to a standard electrical wall junction box 16 (see FIGS. 2 and 3). Hole 14 is elongated to compensate for small errors in alignment of box 16 and the resilient member 12 compensates for errors in mounting of the box 16 which might be behind the plaster and which mounting could result in the humidistat mounting plate 10 being distorted. Fastened through mounting plate 10 is a threaded member 18 carrying knob 19 and a calibrating cam 20 (see FIG. 1A) provided with a projecting stop 20'. Member 18 and cam 20 are held to mounting plate 10 by means of a bushing and nut assembly 22 which also provides a means for zero set adjustment of cam 20. Threaded member 18 is held in position by means for a friction spring 24. Cam 20 is stopped at each end of its 3,123,687 Patented Mar. 3, 1964 rotational travel by means of a stop 26 which, as shown, is a tab cut from plate 10 and which contacts the projection 20'. The humidity responsive element 28 is a cable of human hair which is secured by means of a pair of clamping terminals 30, 32 having ring portions hooked over a switch lever 34 and a setting lever 35, respectively, both of which pivot on a common shaft 37. Element 28 doubles back on itself between its terminals 30, 32 by passing over a roller 29 attached to plate 10. Switch lever 34 engages a switch contact 36 (see FIGS. 2 and 3) forming part of a switch assembly 38 attached to a bracket 39, contact 36 being normally biased against lever 34 by spring means internal of assembly 38. An arcuate relief spring 40 is fastened to plate 10 by inserting a hooked end thereof into a hole 42 and by being passed through a channel 44. The opposite end of spring 40 bears against setting lever 35 and thereby keeps a certain amount of tension on hair element 28. A guard 46 fastened to plate 10 provides protection for the hair element 23 even though the cover plate 48, which is attached to plate 10 by screws 50, 50 engaging tabs 52, 52 is removed.

The device described operates to push switch contact 36 into the switch assembly 38 with shortening (tightening) of the hair element 28 and obviously the switch 38 can be made so that this action either opens or closes the associated circuit. The switch 38 includes an over-center snap switch arrangement and is of a type available on the open market. As the knob 19 is turned in a clockwise direction as seen in FIG. 1, the threaded member 18 moves axially away from setting lever 35, thus permitting spring 40 to force lever 35 upward. The switch member 36 is, therefore, opened and closed at a higher humidity value. If, while the knob is adjusted to a comparatively high humidity value, the relative humidity drops considerably, the hair element 28 will tend to shorten and the tension thereon will increase considerably and could reach such values as to destroy the hair element, except for the fact that such increased tension merely opposes the force exerted by spring 40 and this spring, therefore, provides an upper limit on the force opposing the contractive force of the hair element 28. The spring 40 is designed so that this limit is considerably below that which would destroy or damage hair element 28. As the knob 19 is turned counter-clockwise, the humidity setting is lowered, the member 18 being moved axially against the setting lever 35 causing it to be lowered, slackening the tension in element 28, permitting lever 34 to raise and causing it to be pivoted such as to permit switch member 36 to move out of the switch assembly. When the member 18 has been moved to a very low value, the projecting stop 20 engages an inclined edge 35 on the lever 35 and the hair element 28 is slackened such that the switch contact 36 is positively maintained in its extended position by its internal biasing means. In the present instance this constitutes a positive off position for the switching mechanism.

It will be observed that the device provided is compact and requires very little depth, other than for the part of the switch mechanism which fits into the standard junction box. Consequently, the installation projects only slightly from the wall in which it is installed. It is self-protecting so far as the hair element is concerned because of the relief spring 40, which sets an upper limit on the tension to which the hair element may be subjected. It has been found that a relief spring of this configuration has a substantially constant spring force throughout the useful length of travel of the setting lever 35 and, therefore, complicated means for insuring that the spring is always operating in the same narrow part of its travel are not required Its effect on the hair element is substantially the same irrespective of the setting of the knob 19. This spring also acts as the biasing means for maintaining the hair element 28 in tension.

ing,

While only one embodiment has been shown and described herein, modifications may be made without depart-, ing from the spirit and scope of the present invention.

We claim: 1. In a humidity control device adapted for wallmounta substantially fiat base member adapted to be mounted substantially parallel with said wall,

a roller secured to the outside surface of said base member,

a humidity responsive element mounted on the outside surface of said base member and doubled over said roller in a plane substantially parallel to the plane of said base member, said element changing in l'engthas the moisture content of the surrounding air changes,

a control shaft rotatably mounted on said base and extending perpendicularly therefrom and'a cam'on said shaft behind said base member,

actuator means mounted at the back of said base member including spring biased electrical switchnieans, a first lever operating said switch means against its spring bias and connected to one end of said humidity element, a second lever movable in' response to rotation of said shaft and connecte'dto the opposite end of said humidity element whereby the position of said second lever determines'the operating point of said electrical switch meansrelative to the length of said humidity element,

and an elongated arcuate strain release spring connected between an anchor point on said base and said second lever, whereby upon the tension of said element eX- ceeding a predetermined value, said, second lever is permitted to :move in a direction to reduce the tension on said humidity responsive element, said spring having a substantially constant spring force over the extent of its deflection.

2. In a humidity control device adapted for wall mounta substantially fiat base member adapted to be mounted substantially parallel with said wall,

a humidity responsive element mounted on the outside surface of said base member, said element changing in length as the moisture content of the surrounding air changes,

a control shaft rotatably mounted on said base and extending perpendicularly therefrom and a cam memher having a projection carried on said shaft,

stop means secured with respect to said base member for coacting with said pro'jection'to act as a stop on the rotation of said shaft in both directions,

actuator means mounted at the back of said base member including spring biased electrical switch means,

. a first lever operating said switch means against its spring bias and connected to one end of said humidity element, a second .lever movable in response to rotation of said shaft and connected to the opposite end of said hu'midity'element whereby the position of said second lever determines the operating poin't'of said electrical switch means relative to the length of said humidity element, said second lever including an inclined edge portion cooperating with said cam projection to move said second lever ina direction to substantially reduce the tension on said element such that said switch member is positively held in one of its control conditions,

and an elongated arcuate strain release spring connected between an anchor point on said base andsaid second lever, whereby uponthe tension of said element exceeding a predetermined value, said second lever is permitted to move in a direction to reduce the tension on said humidity responsive element, said spring having a substantially constant spring force over the extent of its deflection.

Sharp Mar. 24, 1936 Kjellman et al.' July 1959 

1. IN A HUMIDITY CONTROL DEVICE ADAPTED FOR WALL MOUNTING, A SUBSTANTIALLY FLAT BASE MEMBER ADAPTED TO BE MOUNTED SUBSTANTIALLY PARALLEL WITH SAID WALL, A ROLLER SECURED TO THE OUTSIDE SURFACE OF SAID BASE MEMBER, A HUMIDITY RESPONSIVE ELEMENT MOUNTED ON THE OUTSIDE SURFACE OF SAID BASE MEMBER AND DOUBLED OVER SAID ROLLER IN A PLANE SUBSTANTIALLY PARALLEL TO THE PLANE OF SAID BASE MEMBER, SAID ELEMENT CHANGING IN LENGTH AS THE MOISTURE CONTENT OF THE SURROUNDING AIR CHANGES, A CONTROL SHAFT ROTATABLY MOUNTED ON SAID BASE AND EXTENDING PERPENDICULARLY THEREFROM AND A CAM ON SAID SHAFT BEHIND SAID BASE MEMBER, ACTUATOR MEANS MOUNTED AT THE BACK OF SAID BASE MEMBER INCLUDING SPRING BIASED ELECTRICAL SWITCH MEANS, A FIRST LEVER OPERATING SAID SWITCH MEANS AGAINST ITS SPRING BIAS AND CONNECTED TO ONE END OF SAID HUMIDITY ELEMENT, A SECOND LEVER MOVABLE IN RESPONSE TO ROTATION OF SAID SHAFT AND CONNECTED TO THE OPPOSITE END OF SAID HUMIDITY ELEMENT WHEREBY THE POSITION OF SAID SECOND LEVER DETERMINES THE OPERATING POINT OF SAID ELECTRICAL SWITCH MEANS RELATIVE TO THE LENGTH OF SAID HUMIDITY ELEMENT, AND AN ELONGATED ARCUATE STRAIN RELEASE SPRING CONNECTED BETWEEN AN ANCHOR POINT ON SAID BASE AND SAID SECOND LEVER, WHEREBY UPON THE TENSION OF SAID ELEMENT EXCEEDING A PREDETERMINED VALUE, SAID SECOND LEVER IS PERMITTED TO MOVE IN A DIRECTION TO REDUCE THE TENSION ON SAID HUMIDITY RESPONSIVE ELEMENT, SAID SPRING HAVING A SUBSTANTIALLY CONSTANT SPRING FORCE OVER THE EXTENT OF ITS DEFLECTION. 